Electron discharge device



June 2,. 1942. A. v. HAEFF ELECTRON DISCHARGE DEVICE Filed Aug. 31, 1939[Sheets-Sheet 1 INVENTOR. ANDREW V. HAEFF ATTORNEY.

June 2, 1942.

A. v. HAEFF ELECTRON DISCHARGKDEVICE 2 Sheets-Sheet 2 Fild Aug. 51, l939 RF m I IIIII/III/IfIIIIIIIIII m M C 1% m 0 w Y B w vw 33 E 8 W s m Wm? P k Kw W W H AG QQ m5 5 m Q mm ww I mm R mm. mm R NMSQQQN ATTORNEY.

Patented June 2, 1942 ELECTRON DIS GE DEVICE Andrew V. Haefi, EastOrange, N. 3., assignor to Radio Corporation of America, a corporationof Delaware Application August 31, 1939, Serial No. 292,812

11 Claims.

My invention relates to electron discharge devices, particularly to suchdevices suitable for use at high frequencies.

It is well known that conventional tubes become inoperative at very highfrequencies. The principal diiiiculties which prevent operation at highfrequencies are due chiefly to the following factors, that is, thefinite electron transit time producing abnormal loading of the inputcircuit and loss of trans-conductance of the tube, difliculty inobtaining necessary small coupling be tween the output electrode and theinput electrode which results in regeneration or excessive loading ofthe output circuit due to the reflected input losses and the consequentloss of power output and efiiciency, and increased losses in the circuitdue to the presence of large circulating currents at high frequenciesand due to an increase in efiective resistance of the circuit.

In my copending application, Serial No. 254,239, filed February 2, 1939,and assigned to the same assignee as the present application, I describeand claim an improved electron discharge device particularly suitablefor use at high frequencies, and in which electron transit time is notcritically related to the period of oscillation, which will functionsatisfactorily at frequencies at which conventional tubes fail tooperate, and in which high frequency losses are minimized, and which isalso particularly suitable for use as an amplifier at very highfrequencies.

In electron beam tubes of this type designed for high frequencyoperation and using, for example, accelerating electrodes and acollector, it is advantageous to utilize electrons of high velocity inorder to reduce transit time through the active spaces of the tube. Thisnecessitates the use of a high potential on the accelerating electrodes.However, for the purpose of obtaining high efiiciency the collectorelectrode is usually operated at a potential below the potential of theaccelerating electrodes, the value of the required collector potentialbeing determined primarily by the high frequency potentials. Thiscondition establishes electric fields near the collector which tend todraw the secondary electrons that may be generated by impact of theprimary electrons on the collector from the collector toward the activespaces of the tube. The secondary electrons returning to the active highpotential accelerating electrodes, thus increasing the dissipation atthe accelerating electrodes and loading the high voltage power supply.

It is therefore the principal object of my invention to provide animproved electron discharge device of the beam type particularlysuitable for use at high frequencies and in which secondary emissioneffects are substantially reduced.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawings in whichFigures l to 4 inclusive are schematic diagrams illustrating theprinciples of my invention, Figure 5 is a simplified diagrammaticrepresentation of an electron discharge device of the type underconsideration, Figure 6 is a sectional view of the collector electrodeillustrating the problem to which applicants invention is directed,Figures 7, 8 and 9 are sectional diagrammatic representations of thecollector electrode construction forming part of applicants inventionfor reducing secondary emission effects, and Figure 10 is a longitudinalsection of an electron discharge device made according to my inventionand its associated circutis and voltage sources.

A better understanding of my present invention can be had by discussingthe principles involved in electron discharge devices of the kind underconsideration. One such device is described and claimed in my copendingapplication above referred to. Reference is had to Figures 1 to 4inclusive. In Figure 1 is schematically shown the longitudinal schematicsection of a quarter wave concentric line tank circuit comprising aninner tubular conductor 20 which may be cylindrical in cross section,and a hollow outer tubular conductor 2| concentric with the innerconductor 20 and electrically connected to the inner conductor 20 by theconducting plat 22.

A second tubular conductor 24 which may be referred to as the apertureextension is coaxial with the conductor 20 and spaced axially fromspaces tend to abstract energy from the high frequency circuits and thusreduce the high frequency output power. Furthermore these secondaryelectrons may be finally absorbed by the the conductor 20 to provide agap 25. This tubular conductor 24 and the outer conductor 2! areconnected by the conducting plate 23. This arrangement provides aquarter wave concentric tank circuit. If a negatively charged body 26 isprojected axially through the inner conductor 20 from left to right, theconditions of the charge distribution on the circuit as the body 26 ismoved along the interior of conductors 20 and 24 is indicated in Figures1 to 4 inclusive. As shown in the figures. there is a positive charge,

equal t th negative charge induced on the in-,'

side of the .innerconductor/near the body.

an electrode arrangement of a tube embodying my invention and operatingon the principledescribed above. Mountedwithin the inner con- However,initially no charge appears on the outer surface of theinner' conductor20. The induced charge moves withthe charged body along the ductor 20 isa conventional cathode 30 and a grid 3|, which supply the pulses ofelectrons in the proper phase relation necessary-to excite the tankcircuit. A collector electrode 32 may be placed beyond the screeningelectrode or aperinner surface of conductor 20 until the end ofconductor 24 as shown in Figure 2. The passage of the charged bodybeyond the gap 25 into the conductor 24 causes the induced charge all toappear on the inner surface of the conductor 24 as shown in Figure 3.The induced charge in transferring from the end of the inner conductorto the conductor 26 flows back over the outer surface of the innerconductor 20 and the inner surface of conductor 21!, thus constituting acurrent flow in the quarter-wave tank circuit. If charged bodies areprojected past the gap in proper phase and frequency relationship withreture extension 24'. If now a high potential is applied between thecathode and the tank circuit including electrodes and 24' and alsobetween the collector 32 and cathode 30, a stream of electrons from thecathode will fiow toward the collector. If a high frequency voltage isapplied between the control grid and the cathode the electron streamwill be periodically moduspect to the resonant frequency of the tankcircuit, the circuit may be made to oscillate vigorously merely by thepassage of the charged bodies past the gap.

Figure 4 illustrates the configuration of the electric and magneticfields within the resonant space of the tank circuit when the latter isexcited. The solid lines 2! represent the electric field distributionand the circles 28 represent the magnetic lines of force. The dashedlines 29 represent the equipotential surfaces in the gap. Along themajor part of the length of the tank circuit the direction of theelectric field is substantially radial. However, at the gap the electricfield has an axial component. The electric field does not penetrate veryfar inside the open end of the inner conducting member 20 or inside theconductor 24, but is confined effectively to the space definedapproximately by the limiting equipotential lines 29 shown in thefigures. The space inside the inner conductor 28 and inside theconductor 24 is essentially field free, therefore no work will be doneon a charge moving inside the inner conductor 20 by the electric fielduntil the charge reaches the gap 25. If the charge traverses the gap atthe instant when the electric force is in the direction from 20 to 24,the charge will be decelerated, its energy being given up to the tankcircuit. A charge crossing the gap during the opposite half cycle whenthe field is reversed will be accelerated and absorb energy from thecircuit. If, however, the number of charges traversing the gap duringthe first half cycle is greater than during the second, the net eifectwill be that energy is supplied to the tank circuit.

Thus, the tank circuit may be excited by passing groups of electrons atthe proper frequency across the gap between the conductors 20 and 24.The motion of the electrons in the interior of the inner conductor 20has no effect on the current in the tank circuit. Also high frequencyelectromagnetic fields which will be generated within the resonantingspace of the tank circuit penetrate but a short distance inside theconductor 20 and conductor 24 which act as a screen electrode so thatthe electrons will be influenced by these fields only during theirpassage across the gap.

lated in intensity. Pulses of electrons traversing the gap 25 willinduce high frequency currents. between the electrodes 20 and 2%. If theexcitation frequency is adjusted to the resonant frequency of the tankcircuit a high impedance will exist across the gap 25 at this frequency.The induced currents, therefore, will produce a high radio frequencyvoltage across the gap 25. The phase of this voltage at or nearresonance will be such as to decelerate electrons traversing the gapduring the half period of maximum intensity of the electron current inthe stream.

The energy lost by the electrons is transformed by the tank circuit intothe energy of the electromagnetic field within the resonating spacebetween the inner and outer conductors and then may be conveyed to theuseful load by means of a coupling loop such as, for example, 33extending through an aperture in the outer tubular conductor 2! of thetank circuit.

The high frequency electromagnetic field existing in the resonant spaceof the tank circuit penetrates only a short distance inside the tubularelectrode 20 and inside the tubular screen electrode 24. Therefore, bypositioning the control electrode 3i at a suitable distance from the gap25 the coupling between the input electrodes 30 and 3! and the outputelectrodes 20 and 24' can be reduced to a negligible value. Thecollector electrode is also placed at an adequate distance from the gapto minimize coupling between it and the tank circuit. This results in areduction of the losses caused by the absorption of radio frequencyenergy from the tank circuit by the collector.

To minimize the transit time effects the electrodes 20 and 24' can beoperated at suitable high potentials with respect to the cathode. Theadjustment of these potentials is not critical because the functioningof the tube does not depend critically upon the electron transit time.This is because the electrons are efiective in exciting the outputcircuit only during the short period of time that they pass through thefield extending through the gap 25. The current collecting electrode 32can be operated at a much lower potential than the conductors 20 and 24In Figure 5 is shown schematically in section and in order to obtain ahigh efiiciency it is usually operated at a potential just suflicient tocollect all decelerated electrons. To improve the -functioning ofthedevice an electrostatic or magnetic focusing of the electron stream canbe utilized to prevent electrons from impinging on the high potentialelectrodes 20 or 24. Thus these electrodes will not dissipate energy andall of the power generated in the tube will be supplied by the lowvoltage collector power supp y.

In electron discharge devices of the kind under consideration whereelectrostatic focusing or focusing by means of short magnetic lenses isutilized, the electrons may enter the collector regions at anappreciable angle to the axis and strike the collector near the entrancewhere there exists an appreciable electric field due to the electrode241 which acts as an accelerating electrode. This tends to acceleratethe secondary electrons away from the collector electrode 32 as shown inFigure 6 by the dotted lines. Also, the angular divergence of theentering beam produces an appreciable distribution of electron velocityin the forward direction, thus necessitating higher collectingpotentials. In order to suppress secondaries it is necessary toestablish a suppressing field near the entrance to the collectorelectrode.

While the electron beam may be held from diverging by a strong magneticfield and the space charge of the beam itself, which establishes asuppressing field near the surface of the collector thus preventing theescape of secondaries if the automatic space charge suppression isinsumcient, the collecting part of the collector may be held at apotential higher than the cylindrical part. As is shown in Figure 8 thecylindrical part 34 is made separate from the collecting part 35. Thecylindrical part will then act as a suppressor electrode. However, whereit is not desired to use such strong electromagnetic fields and where itis not desired to use a separate part at a high potential, other formsillustrated below can be used.

Figure 7 illustrates the use of a suppressor electrode 36 in the form ofa ring in front of the collector 32. In this arrangement the suppressorelectrode is maintained at a potential below the collector potential toproduce a suppressing field at the collector.

While the arrangement in Figure 7 reduces the number of secondaries amore effective form of my invention is shown in Figure 9. Here thesuppressor electrode is in the form of a straight rod 40 positionedalong the axis of the collector and. extending through an aperture 39 atthe rear of the collector 31. By supplying cathode or a slightlypositive potential to the rod, a suppressing field is established overthe inner surface of the collector. In addition the entrance portion ofthe collector may be shielded from the accelerating electrode 241 by aninwardly extending radial lip 38 which may be made an integral part ofthe collector 37. The electrons entering the collector are deflected bythe suppressor field towards the cylindrical portion of the collector asindicated by the dotted lines. The danger of reflection from lowpotential regions near the collector is minimized because the deflectingfield directs electrons toward more positive regions.

With the arrangement shown it has been found possible to reducesecondary electron emission current to 3% of the beam current ascompared to 10% if no suppressor is used.

In Figure 10 is shown a tube in longitudinal section embodying apreferred form of my invention. The main body of the tube, whichconstitutes a quarter wave concentric line output tank circuit includesa pair of tubular coaxial members or electrodes 50 and separated axiallyby a gap 49 and electrically connected to a concentric outer cylinder ortubular member 52 by means of end plates 53 and 54. These elements formthe concentric line output tank circuit. The resonant frequency of thetank circuit may be varied by means of the adjustable condenser plate 66movable by-insulated rod 66 toward and from the electrodes and 5| toincrease or decrease the capacity coupling between these two electrodes.The edges of the electrodes 50 and 5| are thickened and rounded as at50' and 5| to prevent excessive radio frequency fields at the gap with aconsequent dielectric loss in the glass envelope 56 housing the cathodeand collector electrodes. To minimize these losses the glass envelopemay be provided with a short section near the gap made of low lossdielectric such as special glass, quartz or ceramic. To provide coolingfor the tube and particularly to effect adequate cooling of the glassenvelope in the region of maximum electric field at the gap a specialcooling arrangement can be provided as shown by providing a reentrantportion 55 contacting the glass envelope and forming with the innertubular members 50 and 5| a hollow tubular casing around the envelopeinto which air can be forced through tubes 55' and 55", as indicated.The whole external concentric line tank circuit and the glass envelopecan be separated at will.

Envelope 56 which fits within the concentric tank circuit is providedwith an indirectly heated cathode 57, control grid 58 having concaveshaped grid wires 59 to act also as a focusing electrode to preventdispersion of the beam through accelerating electrode 60. The controlgrid can be maintained at either control grid potential or any suitablepotential serving to concentrate the electron stream at the start andmaking it possible to use considerably weaker magnetic focus- .ingfields from solenoids 64" and 65 without undesirable current absorptionby the accelerating electrodes 60 and BI positioned between the cathodeand collector electrode 62 supported from the press 63. The reason forusing the accelerating electrodes 60 and GI is to avoid the undesirableeffects of charges on the glass wall due to bombardment by strayelectrons. The electrodes 60 and 6| are positioned at a suitabledistance from the gap 49 between the electrodes 50 and 5| of the outputtank circuit so that the radio frequency fields from the space betweenthe tubular members 50 and 52 do not reach them, and thus electrodes 60and 6| do not form a part of the output circuit and do not carrycirculating currents. The electron stream from the cathode 51 modulatedand focused by grid 58 traverses the gap between electrodes 5|] and 5|and is collected by collector electrode 62.

A parallel wire transmission line comprising tubular conductors 69and!!! tuned by a conducting bridge 7| form the input circuit. Conductor59' connected to the focusing electrode and grid 58 extends throughtubular member 69 and is connected to the voltage sources 58' to providethe biasing voltage for the electrode 58. The tubular member 10 and theinsulated conductor 68 within the tubular member furnish the cathodeheating current from the source of voltage supply 51' and the conductor10 at the same time acts as the cathode lead. Adequate by-passing forhigh frequency currents, is provided by the condenser preferably placedinside the glass envelope and connected between the heater and cathodeleads. Radio frequency coupling between the transmission line conductors69 and 10 and the grid and the focusing electrode is due to the inherentcapacity between these conductors and the insulated leads within thehollow conductor tubes. If necessary, additional condensers for capacitycoupling can be provided between the conductor tubes and the leads.

When a high potential E80 from voltage source 45 is applied between thecathode 51 and the electrodes 50 and 5| and a voltage Ecoll at 56'between the cathode and collector 62 a stream of electrons from thecathode 51 focused by the magnetic field of the solenoids 64' and 65 isprojected toward the collector 62'without impinging on either electrode50 or 5|. If a radio frequency voltage is applied between control grid58 and cathode 51 by exciting the input circuit by coupling loop 12connected to a driver the electron stream will be periodically modulatedin intensity. Pulses of electrons traversing the gap 49 will induceradio frequency currents in the electrodes 50 and 5|. If the excitationfrequency is adjusted to the resonance frequency of the output circuit50, 52 and 5| a high impedance will exist across the gap 49 at thisfrequency. Consequently, currents induced in electrodes 50 and 5| byelectron pulses will produce a high radio frequency voltage across thegap 49. The phase of this voltage at or near resonance will be such asto decelerate electrons passing during the half period of maximumintensity of electron current in the stream. The energy of thedecelerated electrons is converted by the tank circuit into energy ofthe electric and magnetic fields in the resonant space between the inner50 and outer 52 cylinders and then transferred to the useful load by thecoupling loop 52'.

The radio frequency fields penetrate only a short distance inside thetubular electrode 50 and inside the screening electrode 5|, a distanceeffectively less than their diameter so that by positioning the cathode51, control electrode 58 and the collector 62 at suitable distances fromthe gap 49, the coupling between the output tank circuit and these lastthree t o ed electrodes can be made practically negligible. To reduceelectron transit time between the control grid 58 and the gap, theelectrodes 50 and 5| can be operated at suitably high potentials toincrease the speed of the electrons past the gap. However, to obtainhigh efficiency, the collector electrode potential can be adjusted to avalue just sufficient to collect all decelerated electrons and usuallyhas to be only slightly higher than the effective peak radio frequencyvoltage existing across the gap. The adjustment of the acceleratingpotential Etc is not at all critical. It is usually adjusted to such avalue that the transit time of electrons across the effective length ofthe gap (smaller than the diameter of the electrode 50) is a fraction ofa period so that the loss in transconductance due to transit time issmall. With proper design and a sufficient focusing field there is nocurrent to electrodes 50 and 5|, so that these electrodes dissipate noenergy. The power is supplied only by the collector power supply '56.

In accordance with my invention, in the form of collector illustrated inFigure 10 the collector 62 is a hollow cup-shaped member provided withan inwardly extending lip or rim 62. The accelerating electrode 6| issupported from a press by a conductor 6| which also acts as the lead forapplying a positive potential to this electrode preferably of the sameorder as that applied to the electrodes 50, 5| and 52. Insulatinglysupported within the collector 62 is a suppressor electrode 64 in theshape of a ring which may be insulatingly supported from the outside ofthe collector by means of the bead support 65'. Conductor 66 isconnected to this suppressor and to a point at a less positive potentialthan the collector 62. 7. An axially extending rod 61 extends through anaperture 68 in the rear of the collector and is supported from the press63, being connected to a point preferably at cathode potential asindicated. A shield 89' carried by rod 61 covers the aperture 68 toprevent electrons from escaping from the interior of the collector 62. Afield formation is produced within the collector 62 so that primaryelectrons are deflected to the sides as indicated by the dotted lines inFigure 9 and the secondary electrons prevented from leaving by the lowpotential field produced by the electrode 64. In this way substantiallyall the secondary electrons are prevented from leaving the interior ofcollector 62 and interferring with the proper operation of the tube. Theelectrode 64 serves to prevent excessive reflection by the rod which isoperated at cathode potential. This particular arrangement ofapplicant's invention resulted in a reduction of secondary emissioncurrent to less than 1.5% of the beam current.

One sample of a tube made according to my invention has an externalmember 52 of a length of 6" and diameter of 3", the inner tubularmembers 50 and 5| having a diameter just sufficiently large to permitslipping the concentric line unit over the end of the envelope 56 havingan outside diameter of /1". The gap between the inner tubular member 50and 5| was of the order of 1 s".

The dimensions of the improved type of collector electrode in oneembodiment of my invention consisted of a cylinder 1 /2" in diameter and1%" long; the accelerating electrode 6| is /2 in diameter and less than/8" 'wide and the aperture formed by the lip 62 .6" in diameter; thering suppressor 64 .15" wide had a diameter of 1.1"; suppressor rod 61extended within the collector electrode 62. The materials that arepreferably used for the various electrodes are tantalum, carbonizednickel or carbonized nichrome.

The tube was operated under the following conditions: At a frequency of500 megacycles, power output of 10 watts was obtained, the driving powerbeing about 1 watt and the efiiciency about 30%. The acceleratingvoltage applied to electrode 60 and 6| was of the order of 3000 voltsand the collector electrode voltage of the order of 1000 volts. Thecollector current was approximately 30 milliamperes. The current to theaccelerating electrodes was less than 0.5 m. a. when the potential ofthe suppressor ring was 900 volts and the suppressor rod was held atcathode potential. If the suppressors were maintained at collectorpotential so that no suD- pressor action was present the acceleratingelectrode current rose to 3 m. a. This performance which is readilyobtained with a tube made according to my invention contrasts sharplywith tubes and circuits of conventional design when an attempt is madeto operate them at the higher frequencies.

Thus in a tube made according to my invention electron transit timeeffects are minimized by utilizing electrons of high velocity. This isaccomplished without increasing dissipation and loss in efficiency byseparating the functions of the output electrode and current collectingelectrode and by making use of electron focusing. The output-inputcoupling is reduced to a negligible value by screening and separation ofthe electrodes and circuits. The high frequency losses due to highfrequency voltages are minilecting electrode during operation of saidelecmized by current carrying electrodes of large periphery.

In addition to the above advantages high efliciency results due tocollection of the electrons at low velocity and high power output isattained because the collector may be made of adequate size withoutinfluencing the performance of the output circuit. A non-regenerativeamplification is made possible through the reduction of the output-inputcoupling to a negligible value. Secondary emission effects aresubstantially reduced by the use of the arrangements discussed abovethus increasing tube and circuit efl'iciency.

Other uses to which my invention may be put are for example frequencymultiplication and eneration of oscillations.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedwithout departing from the scope of my inventionas set forth in theappended claims.

What I claim as new is:

1. An electron discharge tube including means for projecting a beam ofelectrons, means for modulating said beam of electrons, an acceleratingelectrode for said beam of electrons and a collecting electrode forcollecting the electrons after their passage past said acceleratingelectrode, all said means being in said tube in the order named, saidcollecting electrode comprising an elongated cup-shaped member with itsopen end in position to receive the beam of electrons, and a ring-likeelectrode within said cupshaped member and adjacent the open end thereoffor providing a field at a lower potential than that of said collectingelectrode.

2. An electron discharge tube including means for projecting a beam ofelectrons, means for modulating said beam of electrons, an acceleratingelectrode for said beam of electrons, and a collecting electrode forcollecting the electrons after their passage past said acceleratingelectrode, all said means being in said tube in the order named, saidcollecting electrode comprising i a cup-shaped member with its open endin position to receive the beam of electrons, and electrode meansextending along the axis of and within said collecting electrode forestablishing a field of lower potential than that of said collectingelectrode during operation of said device.

3. An electron discharge tube including means for projecting a beam ofelectrons, means for modulating said beam of electrons, an acceleratingelectrode for said beam of electrons, and a collecting electrode forcollecting the electrons after their passage past said acceleratingelectrode, all said means being in said tube in the order named, saidcollecting electrode comprising a hollow member openat one end with theopen end in position to receive the beam of electrons, a ring-likeelectrode adjacent the open end of said collecting electrode and coaxialwith said collecting electrode for providing a field of lower potentialthan said collecting electrode, and electrode means extending along theaxis of and within said collecting electrode for establishing a field oflower potential than that of said 001- tron discharge device.

4. An electron discharge tube including a pair of tubular coaxialconducting members separated by a gap, 9. source of electrons forprojecting a beam of electrons past said gap, means for modulatingsaidbeam of electrons prior to their passage past said gap, means foraccelerating said beam of electrons, and a collecting electrode forcollecting the electrons after their passage past said gap, all saidmeans being in said tube in the order named, said collecting electrodecomprising a hollow member open at one end with the open end in positionto receive the beam of electrons, an inwardly extending radial liparound the open end of said collecting electrode, a ring-like electrodeadjacent the open end of said collecting electrode and coaxial with saidcollecting electrode for providing a field of lower potential than saidcollecting electrode, and electrode means extending along the axis ofand within said collecting electrode for establishing a field of lowerpotential than that of said collecting electrode during operation ofsaid electron discharge device.

5. An electron discharge tube including a pair of tubular coaxialconducting members separated by a gap, a source of electrons forprojecting a beam of electrons past said gap, means for modulating saidbeam of electrons prior to its passage past said gap, and a collectingelectrode for collecting the electrons after their passage past saidgap, all said means being in said tube in the order named, saidcollecting electrode comprising a cup-shaped member with its open end inposition to receive the beam of electrons, an inwardly extending radiallip at the open end of said cup-shaped member, a ring-like electrodewithin the collecting electrode and adjacent said lip for providing afield of lower potential than that of said collecting electrode.

6, An electron discharge tube including means for projecting a beam ofelectrons, means for modulating said beam of electrons, an acceleratingelectrode for said beam of electrons, and a collecting electrode forcollecting the electrons after their passage past said acceleratingelectrode, all said means being in said tube in the order named, saidcollecting electrode comprising a cup-shaped member with its open end inposition to receive the beam of electrons, a radially inwardly extendinglip at the open end of said cup-shaped member, a ring-like electrodewithin the collecting electrode and adjacent said lip for providing afield of lower potential than the potential of said collectingelectrode, and a rod electrode extending axially of said collectingelectrode and adjacent the closed end of the cup-shaped member butinsulated therefrom for establishing a field of lower potential thanthat of said collecting electrode.

7. An electron discharge tube including a pair of tubular coaxialconducting members separated by a gap, a source of electrons positionedalong the axis of said tubular conducting members for projecting a beamof electrons past said gap, means for modulating said beam of electrons,and a collecting electrode for collecting the electrons after theirpassage past said gap, said collecting electrode comprising a cup-shapedmember with its open end in position to receive the beam of electrons, aradially inwardly extending lip at the open end of said cup-shapedmember, and a rod electrode extending axially of said collectingelectrode and adjacent the closed end of the cup-shaped member butinsulated therefrom for establishing a field of lower potential thanthat of said collecting electrode.

8. An electron discharge tube having a pair of coaxial tubularconducting members separated by a gap, a conducting member surroundingand connected to said pair of tubular conducting members to form anoscillating tank circuit, means positioned along the axes of saidtubular conducting members for projecting a beam of electrons past saidgap, means for modulating said beam of electrons prior to its passagepast said gap, and a collector electrode for collecting electrons on theopposite side of said gap from the electron projecting means, saidcollecting electrode comprising a cup-shaped member with its open end inposition to receive the beam of electrons, an accelerating electrodeoutside of but adjacent to the open end of said cup-shaped member, and aring-like electrode within said cup-shaped member and adjacent the openend for providing a field of lower potential than that of saidcollecting electrode.

9. An electron discharge tube having a pair of coaxial tubularconducting members separated by a gap, a conducting member surroundingand connected to said pair of conducting members to form an oscillatingtank circuit, means positioned along the axes of said tubular conductingmembers for projecting a beam of electrons past said gap, means formodulating said beam of electrons prior to its passage past said gap,and a collector electrode for collecting electrons on the opposite sideof said gap from said electron projecting means, said collectingelectrode comprising a cup-shaped member withits open end in position toreceive the beam of electrons and having an aperture in its closed end,an accelerating electrode outside of but adjacent to the open end ofsaid cup-shaped member, and a ring-like electrode within said cup-shapedmember and adjacent the open end for providing a field of lowerpotential than that of said collecting electrode, and a rod-likeelectrode extending through the aperture in the closed end of saidcollecting electrode and axially thereof but out of contact therewithfor establishing a field of lower potential than the potential of saidcollecting electrode and a shield on said rod outside of said collectingelectrode for providing an electron shield for the aperture in theclosed end of said cup-shaped member.

10. An electron discharge tube having an envelope containing a cathodeand grid for providing a stream of modulated electrons and a collectorelectrode spaced from said cathode and grid for receiving saidelectrons, and a quarterwave concentric line circuit having a pair ofcoaxial tubular members spaced axially to provide a gap surrounding saidenvelope and the discharge path between the cathode and collectorelectrode with the gap between the tubular members intermediate the gridand the collector electrode, said collector electrode comprising acup-shaped member with its open end in position to receive the stream ofelectrons, a ring-like electrode adjacent the open end of saidcollecting electrode for establishing a field at lower potential thanthe potential of said collector electrode, and means extending axiallyof said collecting electrode for establishing a field of lower potentialthan the potential of said collecting electrode.

11. An electron discharge tube having an envelope having a press andcontaining a cathode and grid for providing a stream of modulatedelectrons and a collector electrode spaced from said cathode and gridfor receiving said electrons, and a quarter-wave concentric line circuithaving a pair of coaxial tubular members spaced axially and providing agap surrounding said envelope and the discharge path between the oathodeand collector electrode and with the gap between the tubular membersintermediate the cathode and the collector electrode, said collectorelectrode comprising a cup-shaped member with its open end in positionto receive the stream of electrons and having an aperture in the closedend, a radially extending lip on said collecting electrode at the openend thereof, an accelerating electrode outside of and adjacent the openend of the collecting electrode and coaxial therewith and supported fromthe press in said envelope, a ring-like electrode inside the collectorelectrode and adjacent the open end thereof and insulatingly supportedwithin and adjacent the open end of said collector electrode, aconnection from said ring extending through said press, a rod-likeelectrode extending axially of the collector electrode through theaperture in the closed end of said collector electrode and supportedfrom said press, and a shield carried by said rod for shielding saidaperture and a support in said press for said collector electrode.

ANDREW V. HAEFF.

